High-resolution paleoceanographic, micropaleontological, sedimentological and paleoenvironmental studies of the Middle-Late Pleistocene to Holocene sediments have been carried out in the South Atlantic, tropical Pacific, Black Sea, Barents and Bering Seas. Our results and correlations of paleoceanographic events in remote regions suggest an important role of the Thermohaline Circulation in global teleconnections on glacial-interglacial and millennial scales.

In the Atlantic, we continue reconstructions of erosional-accumulation activity of bottom currents and the resulting contourite sedimentation. In 2017-2020, three expeditions have been organized to collect the sediment cores on the high-resolution seismic profiles from the Tropical and SW Atlantic (Ivanova et al., 2016 a,b, 2018a,b). The evidences of contourite occurrence are also collected on the Ceará Rise, in the Equatorial Mid-Oceanic Channel, in the transform valleys of the Mid-Atlantic Ridge, in the Argentine Basin, and on the terraces of Patagonian Continental Slope. Notably, it was found out that almost the entire northern segment of the Ceará Rise is covered by a vast field of contourite sediment waves (Borisov, 2019). The distribution of sediment wave heights is suggested to be controlled by geostrophic currents of AABW and NADW as well as by processes on the boundaries between water masses.

The detailed stratigraphy has been developed for the Ioffe Drift located to the NE of the Vema Channel on the Antarctic bottom water pathway to the Brazil Basin. Our new data report numerous long- and short-term stratigraphic gaps over the last ~3 Ma. An interval of specific high-amplitude peaks representing abrupt changes in volume MS and XRF variability is identified from 2.51/2.59 to ~1.9 Ma which can likely serve as a regional stratigraphic benchmark in the future studies of deep-sea contourites (Ivanova et al., 2016, 2020). The correlation of three sediment records from the drift suggests that the most pronounced series of hiatuses, associated with enhanced AABW flow intensity occurred from 1.6 to ~0.81 Ma (i.e. roughly, during the Mid-Pleistocene Transition), and from 2.51/2.59 to ~1.9 Ma (i.e. covers the onset of the modern-type deep-water circulation in the South Atlantic). Glacial–interglacial interplay of southern- and northern-origin deep waters in the Sao Paulo Plateau – Vema Channel over the last 167 kyr (Ovsepyan, Ivanova, 2019). The area was bathed by southern-origin deep water masses during MIS 6, 4–2 and MIS 5.4–5.1, whereas a prevalence of northern-sourced waters is reconstructed for interglacials and MIS 5.5 and 1. In the Sao Tome mount area located on the continental rise of the southwestern Brazil Basin, our seisoacoustic, sedimentological and stratigraphic data provide new insight on the formation history of the Upper Quaternary sediment cover and on the interplay between gravity-driven and bottom current related sedimentation processes during the last glacial-interglacial cycle (Borisov et al., 2019).

On the Argentine Continental Slope, our first results from the Piedra Buena Terrace suggested the formation of sandy glauconite contourites most likely during the glacial low stand of the sea level (Murdmaa et al., 2018). The genetic interpretation of the high-resolution seismoacoustic profiles obtained with SES 2000 deep allowed to infer the erosion and accumulation structures created by the along-slope currents of the Antarctic bottom water, and to identify the seismic facies of contourites and gravities. It was shown that the across-slope gravity flows in submarine canyons provide the sediment material for contourite drifts on the Argentine continental margin (Murdmaa et al., 2020). A set of data on mineral and chemical composition of the Late Miocene deposits was obtained in the region of the contourite paleo-channel in the Northern Morocco in cooperation with colleagues from the Royal Holloway, University of London. The obtained results improved lithological description of the studied outcrops and confirmed the significant role of bottom currents in formation of the Late Miocene deposits of the southern Rifian corridor (Borisov et al., 2020).

In the Pacific, our results documented synchronous episodes of upwelling intensification in the Eastern Equatorial Pacific and Southern Ocean indicaing that millennial-scale bioproductivity changes reflect climatic teleconnection between these two regions by means of “oceanic tunnelling”. In the North Pacific, postglacial bioproductivity changes are in line with climate oscillations recorded in the North Greenland Ice Core and transferred to the North Pacific via the atmospheric bridge (Ovsepyan etal., 2018). However, breakdown of stratification, carbon dioxide release into the atmosphere and sea-surface bioproductivity rise occurred in the western Bering Sea during Heinrich I (17.5–17.0 kyr BP). This might result from the upwelling of southern-sourced deep waters which had been developed in the Subarctic Pacific 1–1.5 kyr later than in the Southern Ocean. This seems to reflect the duration of transferring signal from the high latitudes of the Southern Hemisphere to the North Pacific.

In the Bering Sea, mechanisms of terrigenous influx on the Shirshov Ridge are reconstructed involving advection of the suspended matter with surface and intermediate water masses and ice-rafting. The relative role of both mechanisms is evaluated (Murdmaa et al., 2019). It is documented that the grain-size composition of terrigenous component is controlled by climatic variations, sea ice coverage, drift pathways, conditions of fast sea ice melting, and mobility of bottom waters. High concentrations of drifting ice or permanent sea ice cover likely existed above the southern part of the ridge during the second half of the Heinrich 1 event. The low mobility of bottom waters facilitated only the subice hemipelagic sedimentation of fine fractions from the background reserve of suspended matter. A sharp reduction of ice-rafted flux was reconstructed for the Bølling–Allerød warming interval. Bottom currents affected sedimentation in the central part of the ridge during the entire deglaciation (in addition to the second half of the Heinrich 1 event), and in the southern part during the Bølling–Allerød, Younger Dryas, and Early Holocene.

The glacial-interglacial and millennial variability in bioproductivity, bottom-water oxygenation and sedimentation in the Bering Sea during the last two climatic cycles was reconstructed in cooperation with the German colleagues (Ovsepyan et al. 2017). Relatively high sea surface bioproductivity and reduced sea-ice cover are reconstructed for the penultimate glacial interval, whereas low bioproductivity and expanded sea-ice cover appear to be typical for the last glacial. Millennial-scale changes in intermediate water ventilation are inferred from faunal records for the middle part of the penultimate glacial. High-amplitude environmental variability during the penultimate glacial time in the Bering Sea resembles the well-known Dansgaard-Oeschger oscillations, and roughly corresponds to similar rapid climatic fluctuations found in North Atlantic records. Our results provide support for a close circumpolar coupling between high-latitude environments on millennial timescales at least since the penultimate glacial.

In the northwestern Barents Sea, we investigated the timing, succession, and mechanisms of the transition from proximal glaciomarine to marine environment in cooperation with foreign colleagues (Ivanova et al., 2019). Two studied sediment cores demonstrate diachronous retreat of the grounded ice sheet from the Kvitøya Trough to Erik Eriksen Trough. At the former location, subsurface Atlantic water penetration increased during the Allerød and YD/Preboreal transition. In the study area, foraminiferal and dinocyst data from the YD interval suggest cold conditions, extensive sea-ice cover, and brine formation, along with the flow of chilled AW at subsurface and the development of a high-productivity polynya in the Erik Eriksen Trough. Dense winter sea-ice cover with seasonal productivity persisted in the Kvitøya Trough area during the early Holocene, whereas surface warming seems to have occurred during the middle Holocene interval. In the northeastern Barents Sea, the first decadal to centennial–scale resolution record is reported on foraminiferal and dinocyst assemblages from in the hard-to-reach Cambridge Strait, Franz Josef Land, and on corresponding paleoenvironments over the last 9.2 ka (Ivanova et al., 2020).

On the NE Black Sea outer shelf, the modern species information collected from samples with living fauna was used to interpret the fossil Holocene assemblages of ostracods (Zenina et al., 2017). The alteration of three major types of fossil assemblages is reported demonstrating a gradual transition from the dominance of Caspian species to modern marine fauna. It is very likely that the dominant control of ostracod species occurrence during the period up to ~6.8 cal ka BP is salinity. A range of factors including temperature, biotope, and sedimentation rates influenced the species distribution over the last 6.8 cal ka BP. An integrated Holocene record of marine and terrestrial palaeoenvironmental change from the NE Black Sea shelf has been developed in cooperation with the British partners.